The present invention is in the field of battery technology and, more particularly, in the area of high-energy materials for use in electrodes in electrochemical cells.
Lithium metal oxides have been used to formulate cathode materials for lithium ion batteries. The cathodes are derived from a few basic crystallographic structure types, such as spinels, olivines, and layered oxide structures. The layered oxide structures have included lithium-excess type structures, where additional lithium is present in the structure.
Recently, attention has been focused on rock salt structures, such as those formed from particular lithium metal oxides. Compounds represented by the formula:xLi3NbO4.(1−x)LiMO2  (1)where M is a trivalent cation, have been shown to be a promising class of transition metal oxides for use as cathodes in lithium ion batteries. The compounds of formula (1) are considered a disordered rock salt in which a random atomic arrangement of lithium and transition metal ions are packed in a cubic closed packed system. These disordered rock salt compositions offer the ability to contain up to 3 lithium atoms per formula unit, which is more than the conventional lithium-excess layered materials. Formula (1) can be transformed and represented as LixMyNzOw.
The disordered rock salt structure has the following advantages and challenges when used as a lithium ion battery cathode material. Advantageously, the disordered rock salt structure has significantly higher theoretical energy density as compared to other state-of-the-art cathode materials. For example, certain disordered rock salt structure materials have a theoretical gravimetric energy density of about 1120 Wh/kg, while a LiMn2O4 active material has a theoretical gravimetric energy density of about 492 Wh/kg and a LiMn1.5Ni0.5O4 has a theoretical gravimetric energy density of about 691 Wh/kg. This energy density is especially appealing when manganese is used as a major component, as the disordered rock salt structure achieves this higher energy density using the comparatively lower cost raw material of manganese. That is, compounds with comparable energy density use higher cost raw materials.
Included among the research on disordered rock salt for use in lithium ion batteries is Wang, R.; Li, X.; Liu, L.; Lee, J.; Seo, D.-H.; Bo, S.-H.; Urban, A.; Ceder, G. A Disordered Rock-Salt Li-Excess Cathode Material with High Capacity and Substantial Oxygen Redox Activity: Li1.25Nb0.25Mn0.5O2. Electrochem. Commun. 2015, 60, 70-73. In this publication, a disordered rock salt compound having the formula Li1.25Nb0.25Mn0.5O2 was synthesized and tested. This material demonstrated higher capacity than the theoretical capacity based on the Mn3+/Mn4+ redox reaction. This publication demonstrates the utility of the Li1.25Nb0.25Mn0.5O2 disordered rock salt. However, the embodiments disclosed herein provide variations in the disordered rock salt structure and composition that are not disclosed or suggested in this publication.
Another example of research on disordered rock salt for use in lithium ion batteries is Yabuuchi, N.; Takeuchi, M.; Nakayama, M.; Shiiba, H.; Ogawa, M.; Nakayama, K.; Ohta, T.; Endo, D.; Ozaki, T.; Inamasu, T.; et al. High-Capacity Electrode Materials for Rechargeable Lithium Batteries: Li3NbO4-Based System with Cation-Disordered Rock Salt Structure. Proc. Natl. Acad. Sci. 2015, 112, 7650-7655. This publication discloses the performance of a few compositions of the formulas Li1.3Nb0.3Mn0.4O2, Li1.3Nb0.3Fe0.4O2, Li1.3Nb0.43Ni0.27O2, and Li1.3Nb0.43Co0.27O2. Thus, this publication demonstrates some performance attributes of the disordered rock salt compositions with some variation in the “3d” metal (as defined below), but does not disclose or suggest the variations in the disordered rock salt structure and composition of the embodiments disclosed herein.
Yet another example of research on disordered rock salt for use in lithium ion batteries is Ceder, G.; Lee, J.; Li, X.; Kim, S.; Hautier, G. High-Capacity Positive Electrode Active Material. US 2014/0099549, Apr. 10, 2014. This publication discloses a generic disordered rock salt composition of the LixMyO2 where 0.6≤y≤0.85; 0≤x+y≤2; and M is one or more of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and Sb. However, the embodiments disclosed herein provide variations in the disordered rock salt structure and composition that are not disclosed or suggested in this publication.
Still another example of research on disordered rock salt for use in lithium ion batteries is Takeuchi, M.; Yabuuchi, N.; Komaba, S.; Endo, D. Active Material For Nonaqueous Electrolyte Electricity Storage Elements. US2016/049640, Feb. 18, 2016. This publication discloses a generic disordered rock salt composition of the Li1+xNbyMezApO2 where Me is a transition metal including Fe and/or Mn; 0.6<x<1; 0<y<0.5; 0.25≤z<1; A is an element other than Nb and Me; and 0≤p≤0.2. However, the embodiments disclosed herein provide variations in the disordered rock salt structure and composition that are not disclosed or suggested in this publication.
Embodiments disclosed herein are capable of, and in certain cases have demonstrated, improved capacity, energy density, voltage fade, rate performance, and capacity retention as compared to known disordered rock salt compositions.